Experimental Research And Computer Simulation On Dynamic Responses Of Free-Free Tubes Impacted Laterally

In this paper, experimental researches and computer simulations are presented on dynamics behaviors of free-free tubes laterally impacted by flat-nosed cylindrical missiles at the middle of their spans. To free-free tubes with different diameters, lengths and material properties, their deformation processes, final modes and energy distributions are studied. Simultaneously, the critical velocities are obtained when penetration occurs.In the experiment, two kinds of tubes with alternative diameters and material properties, and three kinds of flat-nosed cylindrical missiles with same length and various diameters are applied. Two classes including six operating modes are designed in the experiment. It can be observed from experiment that the final whole deformations of the tubes take on the shapes of "V", and "W" in certain condition. The local dents of the tubes are obvious. The critical velocities and plugging modes of penetrations can be obtained.In the computer simulation, the finite element program LS-DYNA was used to simulate six operating modes of experiment. The results from simulation are compared with those of experiment. Some phenomena are obtained, which haven't been observed in the experiment. It can be seen from the deformation courses of the tubes that the local dents firstly occur at the beginning of impact. With the growth of the dents, the stiffness decreases, and therigid-body translations and the whole deformations take place. The initial kinetic energy of the missile decreases rapidly to approximate zero during the course of impact, and the energy is transferred to internal energy and kinetic energy of the tube. The internal energy of the tube has the proportion of 80%, and the kinetic energy 20%, which is opposite to that of a free-free beam. The cause is that during the course of local dent, a large amount of energy is dissipated at the moment of impact.In summary, when it is laterally impacted by flat-nosed rigid cylindrical missile at the center, the deformation course, final mode, local dent and energy distribution of a free-free tube are different from those of a free-free beam and a supported tube. The main influent factors include material properties, the proportion of diameter to thickness and diameter to length, and the proportion of diameter of missile to that of tube. When yield limit is low but ultimate strength high, the proportion of diameter to thickness is small but the proportion of diameter to length large, and the proportion of diameter of missile to that of tube is also large, the deformation course, final mode and local dent of the free-free tube are close to those of free-free beam. In contrast, when yield limit is high but ultimate strength low, the proportion of diameter to thickness and diameter to length of tube is large, and the proportion of diameter of missile to that of tube is small, the deformation course, final mode, local dent and energy distribution of the tube are close to those of supported tube.